iwlwifi: mvm: Add preemptive flag to scheulded scan

Add preemptive flag to scheduled scan command flags. Without this
flag, all scan requests after scheduled scan was started will be
delayed until scheduled scan stops. As a result, P2P_FIND will be
blocked while scheduled scan is active.
This flag was omitted during refactoring.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>